condensing the steam having been published in the _Actæ
Eruditorum_, in Latin, in 1690, and in French, at Cassel, in 1695,
and subsequently, in the _Philosophical Transactions_, in England
in 1697, cannot be supposed to be unknown to Dr. Hooke; and if
known to him, would probably have been communicated to Newcomen.
Dr. Hooke died in 1703, some years before the date of Newcomen's
invention.
John Cawley, who was the associate of Newcomen in his experiments
and inquiries, was a plumber and glazier of the same town.
Newcomen and Cawley obtained a patent for the atmospheric engine
in 1705, in which Savery was associated, he having previously
obtained a patent for the method of producing a vacuum by the
condensation of steam, which was essential to Newcomen's
contrivance. It was not, however, until about the year 1711 that
any engine had been constructed under this patent.
In the latter end of that year, according to Desaguliers, the
patentees "made proposals to drain a colliery at Griff, in
[Pg065] Warwickshire, in which work five hundred horses were
constantly employed. This proposal not being accepted, they
contracted, in the following March, to drain water for Mr. Back of
Wolverhampton, where, after many laborious attempts, they
succeeded in making their engine work; but not being either
philosophers to understand the reason, or mathematicians enough to
calculate the power and proportions of the parts, they very
luckily, by accident, found what they sought for."
[Illustration: _Fig._ 14.]
Newcomen resumed the old method of raising the water from the
mines by ordinary pumps, but conceived the idea of working these
pumps by some moving power less expensive than that of horses. The
means whereby he proposed effecting this, was by connecting the
end of the pump-rod D (_fig._ 14.) by a chain with the arch head A
of a [Pg066] working-beam A B, playing on an axis C. The other
arch head B of this beam was connected by a chain with the rod E
of a solid piston P, which moved air-tight in a cylinder F. If a
vacuum be created beneath the piston P, the atmospheric pressure
acting upon it will press it down with a force of fifteen pounds
per square inch; and the end A of the beam being thus raised, the
pump-rod D will be drawn up. If a pressure equivalent to the
atmosphere be then introduced below the piston, so as to
neutralise the downward pressure, the piston will be in a state of
indifference as to the rising or falling; and if in this case the
rod D be made heavier than the piston and its rod, so as to
overcome the friction, it will descend, and elevate the piston
again to the top of the cylinder. The vacuum being again produced,
another descent of the piston, and consequent elevation of the
pump-rod, will take place; and so the process may be continued.
Such was Newcomen's first conception of the _atmospheric engine_;
and the contrivance had much, even at the first view, to recommend
it. The power of such a machine would depend entirely on the
magnitude of the piston; and being independent of highly elastic
steam, would not expose the materials to the destructive heat
which was necessary for working Savery's engine. Supposing a
perfect vacuum to be produced under the piston in the cylinder, an
effective downward pressure would be obtained, amounting to
fifteen times as many pounds as there are square inches in the
section of the piston.[12] Thus, if the base of the piston were
100 square inches, a pressure equal to 1500 pounds would be
obtained.
(38.) In order to accomplish this, two things were necessary: 1.
To make a speedy and effectual vacuum below the [Pg067] piston in
the descent; and, 2. To contrive a counterpoise for the atmosphere
in the ascent.
The condensation of steam immediately presented itself as the most
effectual means of accomplishing the former; and the elastic force
of the same steam previous to condensation an obvious method of
effecting the latter. Nothing now remained to carry the design
into execution, but the contrivance of means for the alternate
introduction and condensation of the steam; and Newcomen and
Cawley were accordingly granted a patent in 1707, in which Savery
was united, in consequence of the principle of condensation for
which he had previously received a patent being necessary to the
projected machine. We shall now describe the _atmospheric engine_,
as first constructed by Newcomen:—
The boiler K (_fig._ 14.) is placed over a furnace I, the flue of
which winds round it, so as to communicate heat to every part of
the bottom of it. In the top, which is hemispherical, two
gauge-cocks G G′ are placed, as in Savery's engine, and a _puppet
valve_ V, which opens upward, and is loaded at one pound per
square inch; so that when the steam produced in the boiler exceeds
the pressure of the atmosphere by more than one pound on the
square inch, the valve V is lifted, and the steam escapes through
it, and continues to escape until its pressure is sufficiently
diminished, when the valve V again falls into its seat. This valve
performs the office of the safety-valve in modern engines.
The great steam-tube is represented at S, which conducts steam
from the boiler to the cylinder; and a feeding pipe T, furnished
with a cock, which is opened and closed at pleasure, proceeds from
a cistern L to the boiler. By this pipe the boiler may be
replenished from the cistern, when the gauge cock G′ indicates
that the level has fallen below it. The cistern L is supplied with
hot water, by means which we shall presently explain.
(39.) To understand the mechanism necessary to work the piston,
let us consider how the supply and condensation of steam must be
regulated. When the piston has been forced to the bottom of the
cylinder by the atmospheric pressure acting against a vacuum, in
order to balance that pressure, [Pg068] and enable it to be drawn
up by the weight of the pump-rod, it is necessary to introduce
steam from the boiler. This is accomplished by opening the cock R
in the steam pipe S. The steam being thus introduced from the
boiler, its pressure balances the action of the atmosphere upon
the piston, which is immediately drawn to the top of the cylinder
by the weight of the pump-rod D. It then becomes necessary to
condense this steam, in order to produce a vacuum. To accomplish
this, the further supply of steam must be cut off, which is done
by closing the cock R. The supply of steam from the boiler being
thus suspended, the application of cold water on the external
surface of the cylinder becomes necessary to condense the steam
within it. This was done by enclosing the cylinder within another,
leaving a space between them.[13] Into this space cold water was
allowed to flow from a cock M placed over it, supplied by a pipe
from the cistern N. This cistern is supplied with water by a pump
O, which is worked by the engine.
The cold water supplied from M, having filled the space between
the two cylinders, abstracts the heat from the inner one; and
condensing the steam, produces a vacuum, into which the piston is
forced by the atmospheric pressure. Preparatory to the next
descent, the water which thus fills the space between the
cylinders, and which is warmed by the heat abstracted from the
steam, must be discharged, in order to give room for a fresh
supply of cold water from M. An aperture, furnished with a cock,
is accordingly provided in the bottom of the cylinder, through
which the water is discharged into the cistern L; and being warm,
is adapted for the supply of the boiler through T, as already
mentioned.
The cock R being now again opened, steam is admitted below the
piston, which, as before, ascends, and the descent is again
accomplished by closing the cock R, and opening the cock M,
admitting cold water between the cylinders, and thereby condensing
the steam below the piston.
The condensed steam, thus reduced to water, will collect [Pg069]
in the bottom of the cylinder, and resist the descent of the
piston. It is therefore necessary to provide an exit for it, which
is done by a valve opening _outwards_ into a tube which leads to
the feeding cistern L, into which the condensed steam is driven.
That the piston should continue to be air-tight, it was necessary
to keep a constant supply of water over it; this was done by a
cock similar to M, which allowed water to flow from the pipe M on
the piston.
(40.) Soon after the first construction of these engines, an
accidental circumstance suggested to Newcomen a much better method
of condensation than the application of cold water on the external
surface of the cylinder. An engine was observed to work several
strokes with unusual rapidity, and without the regular supply of
the condensing water. Upon examining the piston, a hole was found
in it, through which the water, which was poured on to keep it
air-tight, flowed, and instantly condensed the steam under it.
On this suggestion Newcomen abandoned the external cylinder, and
introduced a pipe H, furnished with a cock Q, into the bottom of
the cylinder, so that, on turning the cock, the pressure of the
water in the pipe H, from the level of the water in the cistern N,
would force the water to rise as a jet into the cylinder, and
would instantly condense the steam. This method of condensing by
injection formed a very important improvement in the engine, and
is still used.
(41.) Having taken a general view of the parts of the atmospheric
engine, let us now consider more particularly its operation.
When the engine is not working, the weight of the pump-rod D
(_fig._ 14.) draws down the beam A, and draws the piston to the
top of the cylinder, where it rests. Let us suppose all the cocks
and valves closed, and the boiler filled to the proper depth. The
fire being lighted beneath it, the water is boiled until the steam
acquires sufficient force to lift the valve V. When this takes
place, the engine may be started. For this purpose the regulating
valve R is opened. The steam rushes in, and is first condensed by
the cold cylinder. After a short time the cylinder acquires the
temperature of the steam, which then [Pg070] ceases to be
condensed, and mixes with the air which filled the cylinder. The
steam and heated air, having a greater force than the atmospheric
pressure, will open a valve placed at the end X of a small tube in
the bottom of the cylinder, and which opens outwards. From this
(which is called the _blowing valve_[14]) the steam and air rush
in a constant stream, until all the air has been expelled, and the
cylinder is filled with the pure vapour of water. This process is
called _blowing_ the engine preparatory to starting it.
When it is about to be started, the engine-man closes the
regulator R, and thereby suspends the supply of steam from the
boiler. At the same time he opens the _condensing valve_ H[15];
and thereby throws up a jet of cold water into the cylinder. This
immediately condenses the steam contained in the cylinder, and
produces the vacuum. (The atmosphere cannot enter the _blowing_
valve, because it opens _outwards_, so that no air can enter to
vitiate the vacuum.) The atmospheric pressure above the piston now
takes effect, and forces it down in the cylinder. The descent
being completed, the engine-man closes the condensing valve H, and
opens the regulator, R. By this means he stops the play of the jet
within the cylinder, and admits the steam from the boiler. The
first effect of the steam is to expel the condensing water and
condensed steam which are collected in the bottom of the cylinder,
through the tube Y, containing a valve which opens _outwards_
(called the _eduction valve_), which leads to the hot cistern L,
into which this water is therefore discharged.
When the steam admitted through R ceases to be condensed, it
balances the atmospheric pressure above the piston, and thus
permits it to be drawn to the top of the cylinder by the weight of
the rod D. This ascent of the piston is also assisted by the
circumstance of the steam being somewhat stronger than the
atmosphere.
When the piston has reached the top, the regulating valve R is
closed, and the condensing valve H opened, and another descent
produced, as before, and so the process is continued. [Pg071]
The manipulation necessary in working this engine was, therefore,
the alternate opening and closing of two valves; the regulating
and condensing valves. When the piston reached the top of the
cylinder, the former was to be closed, and the latter opened; and,
on reaching the bottom, the former was to be opened, and the
latter closed.
(42.) The duty of working the engine requiring no great amount of
labour, or skill, was usually entrusted to boys, called, _cock
boys_. It happened that one of the most important improvements
which has ever been made in the working of steam engines was due
to the ingenuity of one of these boys. It is said that a lad,
named _Humphrey Potter_, was employed to work the cocks of an
atmospheric engine, and being tempted to escape from the
monotonous drudgery to which his duty confined him, his ingenuity
was sharpened so as to prompt him to devise some means by which he
might indulge his disposition to play without exposing himself to
the consequences of suspending the performance of the engine. On
observing the alternate ascending and descending motion of the
beam above him, and considering it in reference to the labour of
his own hands, in alternately raising and lowering the levers
which governed the cocks, he perceived a relation which served as
a clue to a simple contrivance, by which the steam engine, for the
first time, became an automaton. When the beam arrived at the top
of its play, it was necessary to open the steam valve by raising a
lever, and to close the injection valve by raising another. This
he saw could be accomplished by attaching strings of proper length
to these levers, and tying them to some part of the beam. These
levers required to be moved in the opposite direction when the
beam attained the lowest point of its play. This he saw could be
accomplished by strings, either connected with the outer arm of
the beam, or conducted over rods or pulleys. In short, he
contrived means of so connecting the levers which governed the two
cocks by strings with the beam, that the beam opened and closed
these cocks with the most perfect regularity and certainty as it
moved upwards and downwards.
Besides rendering the machine independent of manual [Pg072]
superintendence, this process conferred upon it much greater
regularity of performance than any manual superintendence could
ensure.
This contrivance of Potter was very soon improved by the
substitution of a bar, called a _plug frame_, which was suspended
from the arm of the beam, and which carried upon it pins, by which
the arms of the levers governing the cocks were struck as the
plug-frame ascended and descended, so as to be opened and closed
at the proper times.
The engine thus improved required no other attendance except to
feed the boiler occasionally by the cock T, and to attend the
furnace.
(43.) However the merit of the discovery of the physical
principles on which the mechanical application of steam depends
may be awarded, it must be admitted that the engine contrived by
Newcomen and his associates, considered as a practical machine,
was immeasurably superior to that which preceded it; superior,
indeed, to such a degree, that while the one was incapable of any
permanently useful application, the other soon became a machine of
extensive utility in the drainage of mines; and, even at the
present time, the atmospheric engine is not unfrequently used in
preference to the modern steam engine, in districts where fuel is
abundant and cheap; the expense of constructing and maintaining it
being considerably less than that of an improved steam engine. The
low pressure of the steam used in working it, rendered it
perfectly safe. While Savery's engine, to work with effect,
required that the steam confined in the vessels should have a
bursting pressure amounting to about thirty pounds per square
inch, the pressure of steam in the boiler and cylinder of the
atmospheric engine required only a pressure about one pound per
square inch. The high pressure also of the steam used in Savery's
engine, was necessarily accompanied, as we shall presently
explain, by a greatly increased temperature. The effect of this
was, to weaken and gradually destroy the vessels, especially those
which, like the steam vessels V and V′ (_fig._ 12.), were
alternately heated and cooled.
Besides these defects, the power of Savery's engines was [Pg073]
also very restricted, both as to the quantity of water raised and as
to the height to which it was elevated. On the other hand, the
atmospheric engine was limited in its power only by the dimensions
of its piston. Another considerable advantage which the atmospheric
engine possessed over that of Savery, was the facility with which it
was capable of driving machinery by means of the working-beam. The
merit, however, of Newcomen's engine, regarded as an invention, and
apart from merely practical considerations, must be ascribed
principally to its mechanism and combinations. We find in it no new
principle, and scarcely even a novel application of a principle. The
agency of the atmospheric pressure acting against a vacuum, or
partial vacuum, had been long known: the method of producing a
vacuum by the condensation of steam had been suggested by Papin, and
carried into practical effect by Savery. The mechanical power
obtained from the direct pressure of the elastic force of steam,
used in the atmospheric engine to balance the atmosphere during the
ascent of the piston, was suggested by De Caus and Lord Worcester.
The boiler, gauge pipes, and the regulator, were all borrowed from
the engine of Savery. The idea of using the atmospheric pressure
against a vacuum or partial vacuum, to work a piston in a cylinder,
had been suggested by Otto Guericke, an ingenious German
philosopher, who invented the air-pump; and this, combined with the
production of a vacuum by the condensation of steam, was
subsequently suggested by Papin. The use of a working-beam could not
have been unknown. Nevertheless, the judicious combination of these
scattered principles must be acknowledged to deserve considerable
credit. In fact, the mechanism contrived by Newcomen rendered a
machine which was before altogether inefficient, highly efficient:
and, as observed by Tredgold, such a result, considered in a
practical sense, should be more highly valued than the fortuitous
discovery of a physical principle. The method of condensing the
steam by the sudden injection of water, and of expelling the air and
water from the cylinder by the injection of steam, are two
contrivances not before in use, which are quite essential to the
[Pg074] effective operation of the engine. These processes, which
are still necessary to the operation of the improved steam engine,
appear to be wholly due to the inventors of the atmospheric engine.
[Illustration: ATMOSPHERIC ENGINE.]
FOOTNOTES:
[9] This pipe is represented as proceeding from the force-pipe
above the cistern C, in the perspective view of Savery's
engine at the head of this chapter.
[10] Hot water being lighter than cold, floats on the surface.
[11] "Captain" is a title given in Cornwall to the
superintendent of the works connected with a mine.
[12] As the calculation of the power of an engine depends on
the number of square inches in the section of the piston, it
may be useful to give a rule for computing the number of
square inches in a circle. The following rule will always give
the dimensions with sufficient accuracy:—_Multiply the number_
_of inches in the diameter by itself; divide the product by 14,_
_and multiply the quotient thus obtained by 11, and the result_
_will be the number of square inches in the circle_. Thus, if
there be 12 inches in the diameter, this multiplied by itself
gives 144, which divided by 14 gives 10-4/44, which multiplied
by 11 gives 115, neglecting fractions. There are, therefore,
115 square inches in a circle whose diameter is 12 inches.
[13] The external cylinder is not represented in the diagram.
[14] Also called the _snifting_ valve, from the peculiar noise
made by the air and steam escaping from it.
[15] Also called the _injection valve_.
[Pg075]
[Illustration: GREENOCK, IN 1824.]
CHAP. III.
PROGRESS OF THE ATMOSPHERIC ENGINE. — SMEATON'S IMPROVEMENTS.
— BRINDLEY, ENGINEER OF THE BRIDGEWATER CANAL. — INVENTS THE
SELF-REGULATING FEEDER. — JAMES WATT. — HIS DESCENT AND
PARENTAGE. — ANECDOTES OF HIS BOYHOOD. — HIS EARLY AQUIREMENTS.
— GOES TO LONDON. — RETURNS TO GLASGOW. — IS APPOINTED
INSTRUMENT-MAKER TO THE UNIVERSITY. — OPENS A SHOP IN GLASGOW.
— HIS FRIENDS AND PATRONS. — ADAM SMITH. — DR. BLACK. — ROBERT
SIMSON. — PROFESSOR ROBISON. — WATT'S PERSONAL CHARACTER. —
INDUSTRIOUS AND STUDIOUS HABITS. — HIS ATTENTION FIRST
DIRECTED TO STEAM. — EXPERIMENTS ON HIGH-PRESSURE STEAM. —
REPAIRS AN ATMOSPHERIC MODEL. — EXPERIMENTAL INQUIRY
CONSEQUENT ON THIS. — ITS RESULTS. — DISCOVERS THE GREAT
DEFECTS OF THE ATMOSPHERIC ENGINE. — DISCOVERY BY EXPERIMENT
OF THE EXPANSION WHICH WATER UNDERGOES IN EVAPORATION. —
DISCOVERS THE LATENT HEAT OF STEAM. — IS INFORMED BY DR. BLACK
OF THE THEORY OF LATENT HEAT.
(44.) The atmospheric engine was brought to a state of
considerable efficiency and improvement by Mr. Beighton, in 1718.
From that time it continued in use without any change in its
[Pg076] principle, and with little improvement in its structure,
for half a century. Although engines of this kind continued to be
extensively constructed, they were usually executed by ordinary
mechanics, incapable of applying to them the just principles of
practical science; and, consequently, little attention was paid to
their proportions. It was not until about the year 1772, that Mr.
John Smeaton, the celebrated engineer, applied the powers of his
mind to the investigation of this machine, as he had previously
done with such success to wind and water mills. Although he did
not introduce any new principle into the atmospheric engine, yet
it derived greatly augmented power from the proportions which he
established for engines of different magnitudes.
In 1759, Mr. James Brindley, whose name is so celebrated as the
engineer of the Duke of Bridgewater's canal, obtained a patent for
some improvements in the atmospheric engine. He proposed that the
boiler should be made of wood and stone, with a stove or
fire-place of cast iron within it, so that the fire should be
surrounded on every side by water. The chimney was to be an iron
pipe or tube, conducted through the boiler; so that the heated
air, in passing from the fire, should impart a portion of its heat
to the water. He also proposed a method of feeding the boiler,
which, by self-acting machinery, would keep the water in the
boiler at a fixed level, independently of any attention on the
part of the engine-man. This was to be accomplished by a buoy or
float upon the surface of the water in the boiler, which should
communicate with a valve in the feed-pipe, so that when the level
of the water in the boiler fell, the float or buoy, falling with
it, would open the valve and supply the feed. It is stated, in the
_Biographia Britannica_, that Mr. Brindley, in 1756, undertook to
erect an engine at Newcastle-under-Lyne; but he is said to have
been discouraged by the obstacles which were thrown in his way,
and to have abandoned the steam engine.
The interval between the invention of the atmospheric engine, and
the amelioration it received at the hands of Smeaton, has been
rendered memorable by the advent of one who was destined to work a
mighty change in the condition [Pg077] of the human race by the
application of his vast genius to the adaptation of steam power to
the uses of life.
(45.) JAMES WATT was born at Greenock, in Scotland, on the
nineteenth day of January, in the year 1736.[16]